Electronic tube circuits



June 19, 1945. Q H SCHADE ELECTRONIC TUBE CIRCUIT Filed Jan. 20, 1945/VVE l?! aangaf/im FREQa/EA/c y /Los/ ATTORNEY Patented June 19, 1945`ELECTRONIC TUBECIRCUITS Otto H. Schade, West Caldwell, N. J., assignorto Radio Corporation of America, a corporation of Delaware ApplicationJanuary 20, 1943, Serial No. 472,950

16 Claims. (01.179-171) This invention relates to an improvement intelevision transmitting systems, and more par-V ticularly, to animprovement in the amplifying system associated with a television pickuptube. For the transmission of high fidelity television images, i-t is`desirable tobe able faithfully t'o transmit a very wide range of picturesignals occupying a frequency spectrum of from substantially zero ytofrequencies of the order of 12 to 20 megacycles per second. Furthermore,in order that the reproduced images at the receiver may have the propertonal values and may be of the proper fidelity, it is desirable that allfrequency values within this extremely wide range of frequencies betransmit-ted in their proper intensities. The amplification of such arange of frequencies is exceedingly difficult principally by reason ofthe fact that the circuit elements, which include resistances,condensers and inductances, offerdifferent electrical impedances atdifferent frequencies.

Where a relatively narrow band of frequencies is lto be amplified, aproper choice of the circuit elements may be made in accordance with thedifferent frequencies encountered. However, Where a `Wide frequencyspectrum is to be amplified, it is virtually impossible to select thevalues of the various circuit elements such that attenuation willnot`occur in one or another portion of the frequency spectrum,

In virtually all television pickup tubes, some picture signal outputload impedance must be employed, and some actual or distributed capacityis always present across this load impedance. If the impedance is in theform of a resistance,

the signal strength available at the output e1ec-' trodes ofthetelevision pickup tube Will vary in 'accordance with the frequency ofthe generated picture signals, with the result that a higher picturesignal strength will be present for the stantially linear amplificationfollows, with the result that all of Ithe picture signals, irrespectiverelatively lowpicture signals than is present for the higher frequencypicture signals. This attenuation with increase in frequency is causedprimarily by reason` of the time constant of the output load circuit ofthe television pickup tube.

In order to compensate for lthis attenuation as a function of frequency,compensating networks must be provided, or' the gain of an amplifiertube must be so controlled as to increase the intensity of the picturesignals of relatively high frequency to an extent greater than theincrease 'in intensity of the picture signals of low frequency. When theattenuation and phase shift of the higher frequencies of the picturesignal series is exactly compensated for, subof Itheir position withinthe frequency spectrum, represent their proper intensities in accordance'with the light intensities of the ltelevision image to be transmitted.

The present invention provides a television picture signal amplifiercircuit in which the amplification and phase shift of the picturesignals is controlled as a function offrequency, in order thereby tocompensate for the attenuation and phase shift of the picture signals asa function of frequency caused by the various circuit elements. Whencomplete compensation is accomplished, the picture signal output fromthe television signal amplifier is substantially linear with the resultthat the signal strength and phase delay of the picture signals iscorrect and corresponds to the-particular television image to I betransmitted.

It is, therefore, one purpose of the present invention to provide atelevision transmitting system in which the picture `signal amplifierassociated with the television pickup Itubewill `supply picture signalsbearing the phase relationship Ito the transmitted. l

Another purpose of the present invention resides in the provision of apicture signal amplifier in a television transmitter that is so arrangedto compensate for frequency attenuation caused by the circuit elementsof fthe television system.

Another purpose of the present invention resides in the provision of atelevision picture signal amplifier 'in which a very Wide band offrequencies may be amplified in a linear manner without attenuation atany portion of the band or spectrum as a function of frequency.

A further purpose of the present invention resides in the provision ofan amplifier in a television picture signal amplifier system Vin whichthe amplification of the amplifier tube is controlled in accordance witha function ofthe frequency of the applied signals.

television image to be resides in vthe'provision of an amplifier tube ina television picture signal amplifier channel in which the effectivecathode impedance of the amplifier tube is maintained high, while at thesame time the bias potential between the cathode and control electrodeof the amplifier tube is not excessive.

A still further purpose of the present invention resides in theprovision of an amplifier tube in a picture signal amplifier channelassociated with proper intensity and tube in which the cathode circuitfor the amplil fier tube includes an electron path in order that thecathode circuit may have a relatively high impedance without imposing ahigh bias potential on the control electrode of the amplifier tube.

A further purpose of the present invention resides inthe provision of anamplifier tube in an amplifying channel associated with a televisionpickup tube in which the cathode circuit of the amplifier tube may havean effective high electrical impedance without the necessity ofproviding an auxiliary high potential source.

A still further purpose of the present invention is the provision of oneor more amplifiers in an amplier circuit for a television pickup tube inwhich provision is made to generate an inverse feedback voltage on animpedance in the cathode load circuit of one or more ofthe amplifiersfor obtaining a predetermined gain versus frequency characteristic of'the amplifier circuit, the phase and magnitude of the generatedfeedback voltage being adjustable, and depending on the impedance of thenetwork in the cathode circuit.

Since the impedance of the load circuit of the television pickup tube orthe input circuit of the picture signal amplifier tube may be of theorder of megohms at low frequencies and only several hundred ohms athigh frequencies, a gain variati-on of a range of several thousand timesis, therefore, required to compensate for the impedance variation. Itis, therefore, another purpose of the present invention to compensateperfectly for variations in the impedance of the output circuit of atelevision pickup tube or the input circuit of an amplifier stage topermit substantially linear amplification over a wide frequency bandranging from substantially zero to frequencies of the order of from 12to 20 megacycles per second. l

Still another purpose of the present invention resides inthe provisionof a simple and convenient means in a television picture signalamplifler to adjust -the operation of the amplifier to accommodate widelimits of amplifier input impedance or wide limits of television pickuptube. output impedance without altering the over-all gain or frequencycharacteristics of the amplifier circuit, and without the necessity ofchanging any of the direct current potentials in the amplifier circuit.

form of the present present invention. Referring now to the drawing, andparticularly to Figure 1 thereof, there is shown a television pickuptube I having a target electrode I2 and an output-conductor I4. As iswell known to those skilled in the art, when the target electrode I2 isscanned by a focused cathode ray beam, a series of picture signals isgenerated that may have a wide frequency spectrum ranging fromsubstantially zero frequency to frequencies of the order of 12 or moremegacycles per second. The frequency of the produced picture signals isa function of the number of lines scanned per frame, the fieldrepetition rate and other functions,- as is well known to those skilledin the art.

A load circuit including resistance I 6 is connected between the outputconductor I4 and ground, and between conductor I4 and ground a certainactual or distributed capacity I8 is also present. A potential isdeveloped across resistance I6 and capacitance I8, and this potential isthen applied-to the control electrode of an amplifier tube in order toincrease the amplitude of the produced picture signals. The amplifiertube 20 includes at least a cathode, a control electrode and an anode,and in the particular circuit shown, the cathode is connected to groundwhile the control electrode is connected directly to the outputconductor I4 of the television pickup tube I0. The anode of theamplifier tu-'be 20 is maintained positive by con-- necting the anode toa source of positive potential by means of a peaking circuit 22, aninductance 24 and a resistance 26. The tube 20 will then amplifylinearly the potentials impressed upon the control electrode thereof,and these potentials in amplified form are generally obtained from point28 located between the peaking circuit 22 and the inductance 24.

lThese signals are then applied to the control electrode of a furtheramplifier tube 30 by way of coupling condenser 32. The amplifier tube3l) includes at least a cathode, a control electrode and an anode, andth`e control electrode is connected to ground by grid resistance 34. Thecathode of tube 30 is connected to the negative terminal of a source ofpotential 36 by means of a relatively large resistance 38 and a parallelcondenser 40'. A point along the source of potential 36 (indicatedconventionally as a battery in Figure 1) is connected to ground, and thepositive terminal of the battery 36 is connected to the anode of tube 30by Way of load resistance 42, load impedance 44 and peaking circuit 46'.'Ihe output potentials may then 'be derived between output terminal 48land ground, the output terminal' being connected to the junction of thepeaking circuit 46 and the inductance 44 by way of coupling condenser50.

The voltage developed at the control electrode of tube 20 by thetelevision pickup tube I0 or by any constant current generator having avariable frequency output is proportional to the impedance of thecircuit resistance I6 and capacitance I8, and has a frequencycharacteristic such as that represented by the curve A- in Figure 3. In.

Figure 3 the horizontal or abscissa co-ordinate is graduated as alogarithm scale, and represents the frequency of the produced picturesignals. The vertical or ordinate co-ordinate is also logarithymicallygraduated. It will be noticed by inspecting Figure 3 that the producedpicture signals remain substantially constant in intensity throughout apredetermined frequency range, and above this frequency rangesubstantially constant attenuation of signal strength results. It is,therefore, desired that an amplifier or compensating source, which isnecessary as cathode circuit of tube 30 is so chosen that the timeconstant of this cathode impedance is equal to the time constant of theresistance I6 and capacitance I8, with the resistance 38 equal to Zcqmis the input circuit impedance ratio between zero frequency and thecutoff frequency or maximum frequency Fc of the television picturesignalband, and where gm is the mutual conductance of the `ampliiier tube.Under these conditions the relative input voltage at the controlelectrode of tube 30 (as required for a constant current output of tube30 as a function of frequency) is represented Where by the curve A withthe dotted portion at the higher frequency end of the curve. When theseconditions exist, the corresponding gain characteristics of theamplifier tube 30 will be similar to the curve shown at B in` Figure 3,and will result in the plate load circuit of tube 30 havin,r a linearfrequency characteristic and the output voltage as represented by curve"C will be substantially constant/up to a frequency of 0.3 Fc, at whichfrequency it drops to 94% and then decreases to 66% at the maximumfrequency Fc of,`

the band.

In` order to satisfy the above conditions, it is apparent that the valueof the resistance 38 must be quite high in order to obtain goodcorrection for wide frequency bands, The cathode current of tube 30causes .a voltage drop Ek across resistance 38, and such a voltage dropwould be entirely too great for proper operation of tube 30. In order tooppose the excessive voltage drop, a portion Bk of battery 36 is used sothat the cathode of tube 30 is maintained only slightly positive withrespect to ground potential (or control electrode potential) in order toprovide the proper bias on the control electrode of tube 30. Inasmuch asthe value of the resistance 38 must be exceedingly high, naturally thevoltage drop will be high, and accordingly the potential of the portionBk of battery 36 must be quite high. On -test it has actually been foundthat for a frequency band of 12 megacycles and an input circuitresistance (resistance I6) of one megohm and capacitance (condenser IB)of 25 micro-micro-far- 4ads, the capacity of the condenser 40 should be100 micro-micro-farads and the resistance of the resistor 38 should be250,000 ohms for a tube of the type GAC? as tube 30. When these valuesare used in order-to provide substantially linear ampliiication for afrequency band of the order of 12 megacycles, it is necessary to provideapproximately 2,000 volts for the portion Bk of battery 36 when a normalcathode current of 8 milliamperes is permitted to flow through tube 30.Naturally, such a high potential is difficult to provide, and although`the circuit functions completely satisfactorily to accomplish thedesired purposes of this invention, it nevertheless is not, from thestandpoint of a commercial application, of the usually practicedsimplicity. y i

In order to avoid the use of a high potential explained above, it

is possible to use arl electron current path in the cathode circuit oftube 30 to provide an effective high impedance cathode resistancewithout the necessity of providing a very -high potential source. Anembodiment of such an arrangement is shown in Figure 2 of the drawing.In this iigure, all parts identical to corresponding parts in Figure 1bear similar reference numerals, and in order to avoid repetition, thatpart of the circuit be considerably higher, a parallel adjustablepreceding amplifier tube k will not be again described.

In Figure 2 it will be observed that a pentode 60 is included in thecathode circuit of tube 30. The anode ofthe pentode `6l) is connecteddirectly to the cathode of tube 30, while the cathode '62 of the pentode60 is connected to the negative terminal of a source of potential 64(indicated for convention purposes only as a battery in the drawing) byway of an adjustable resistance 66.

The resistance 66 is provided in the cathode circuit ofthe pentode 60 inorder to afford a biasing potential for tube 60, and it will be observedthat the control electrode of the tube 60 is connected directly to thenegative terminal of the battery A point along the battery is connectedto ground potential, and the positive end of the battery or source ofpotential is connected to the anode load circuit of tube 30. Since it isdesirable to operate thescreen electrode of tube 60 positive relative tothe cathode, the screen is connected to a point correspondingapproximately to the ground point of the source of potential 64.

Inasmuch as the plate impedance of i the pentode 60 may not be theexactvalue required for producing the desired electrical impedance in thecathode circuit of tube 30, and infact may resistance 68 is provided(corresponding to resistance 38 in Figure `1), one end of the resistancebeing connected directly to the cathode of tube 30 and an adjustablepoint along the resistance being connected to ground lby way of acondenser 10, the size of the condenser-1U being chosen such that itoffers relatively low impedance to the frequencies to be amplified. Ashunt condenser is also connected. between the cathode and groundltoform the proper cathode impedance Ze as explained. The condenser 40could as well be connected between `the cathode and the negativeterminal of the source of potential 64.

The inclusion of the pentode in the cathode circuit of tube 30 overcomesthe necessity of providing a high potential source as in Figure 1, sincethe pentode requires a relatively low direct current energizingpotential, yet offers a` relatively high plate impedance which may be ofthe order of from 300,000 ohms to one megohm in practical tubes. Inpractice, it has been found that only a voltage of the order of 150volts is necessary for energizing tube 60, and naturally such apotential is more readily provided than a a potential of the order of2,000 volts as required in the circuit shown in Figure 1. Should theplate impedance of tube 60 .be excessive to produce the desired results,then the parallel resistance 68 may be included and adjusted to providethe desired cathode resistance corresponding to the resistance 38 inFigure 1. The effective value of the cathode resistance for tube 30 isaccordingly the parallelvalue of the plate impedance of the pentode 60and the value of adjustable resistance 68. The cathode resistance 66 forthe pentode 60 may be adjusted to vary the bias of tube 60 in order thatthe correct amount of direct curcuit arrangement shown and claim as newand desire to wide frequency yband may be accomplished. Furthcrmore,this operation is made possible without the introduction of anycomplicated circuit arrangement and without the necessity of providn ingan auxiliary high voltage source.

In actual-practice it has been found that the input resistance (i. e.,the television pickup tube load resistance I6) may be chosen to have avalue ranging from 50,000v ohms to as high as one megohm, and by merelymaking commensurate adjustments in the value of resistance 68, it ispossible to obtain complete correction and constant gain over afrequency band of the order of 12 megacycles per ysecond'or higherregardless of the value of the particular input resistance.

Through the use of the present invention it is, therefore, possible toobtain picture signals of the desired amplitude from the output terminal48 of the amplifier in order that a wide band of frequencies may betransmitted, and in order that the usual attenuation of the highfrequency picture signals will not result.

I t is to ybe appreciated that the particular cirdescribed herein is notnecessarily specifically applicable to the use of television pickuptubes, since the circuit arrangement. may ibe used in connection withany source of signals where a very wide frequency band is encountered. v

Although the present invention has been described in its preferred formin considerable detail, it is to beunderstood that various alterationsand modifications may be made therein without departing from the spiritand scope thereof, and it isldesired that any and all such alterationsand modifications be considered within the purview of the presentinvention, except as limited by the hereinafter appended claims.

Having now described my invention, what I have protected by LettersPatent is: y

1. A television imageAsignal amplifier for amplifying a wide band offrequencies extending from substantially zero to frequencies of theorder of 12 to 20 megacycles per second comprising a signal terminal forsupplying a wide frequency :band of image signals, a load impedanceconnected between the signal terminal and a point of fixed potentialcomprising parallelly connected resistance and capacitance elementsfafirst amplifying means having input and output terminals, means to applythe image signals from the signal terminal to the input terminal of thefirst amplifying means to produce amplified image signals at the outputterminal of said means, a second amplifying means comprising an electrondischarge tube having a cathode, a control electrode and an anode, aresistance connected between said control electrode and'the point offixed potential, means for coupling the output terminal of said vfirstamplifying means to said control electrode, a source of potential havingone terminal positive with respect to the point of fixed potential andanother terminal negative with respect to the point of fixed poandcapacitance elements of the load in parallel with said cathodeimpedance, said cathode impedance having ra value substantially equal tothe ratio of the impedance of the input circuit of the first amplifyingmeans at the low frequency end of the band of image signals to theimpedance of said input circuit at the high frequency end of the band ofimage signals, the product of the cathode impedance and.A its parallelcondenser being substantially equal to the product of the resistanceimpedance, and an output circuit associated with the anode of saidsecond amplifying means.

`2. A signal amplifier for amplifying a wide frequency band of signalsextending from substantially zero to frequencies of the order of manymegacycles per second comprising a source of signals having an outputterminal for supplying such signals, a load impedance connected betweenthe Signal output terminal and a point of fixed potential comprising aresistance and effectively parallelly'connected distributed capacitanceelements, a signal amplifying'means includingan electron discharge tubehaving a cathode, a control electrode and an anode, a resistanceconnected between said control electrode and the point of fixedpotential, means for coupling the source of signals to said controlelectrode, a source of potential having one terminal positive withrespect to the point of fixed potential and another terminal negativewith respect to the point of fixed potential, a load impedance connectedbetween the positive terminal of the source of potential and said anode,a cathode impedance connected between the negative terminal of thesource of potential and said cathode, a condenser effectively connectedin parallel with said cathode impedance, said cathode impedance having avalue substantially equal to the ratio of the effective impedance of thesignal output terminal load impedance at the low frequency end of theband of signals to t/he effective impedance of the signal outputterminal load impedance at the high frequency end of the band ofsignals, the product of the cathode impedance and its parallel condenserbeing substantially equal to the product of the load resistance andcapacitance at the signal source output terminal, and an output circuitassociated with the anode of said second amplifying means.

3. A television signal amplifier for amplifying a Wide frequency band ofsignals comprising a signal output terminal, for supplying the widefrequency band of signals, a first amplifying means having an inputcircuit andan output circuit, said input circuit including parallellyconnected resistance and capacitance elements connected between thesignal output terminal and a point of fixed potential, means to applythe signals from the signal output terminal to the input circuit of thefirst amplifying means to produce amplied signals in the output circuitof said means, a second amplifying means comprising an electrondischarge tube having a cathode, a control electrode Vand an anode, aresistance connected between said control electrode and the point offixed potential, means for coupling the output circuit of said firstamplifying means to said control potential having positive and negativeterminals electrode, a source of v means for connecting `a point alongsaid source of potential to the point of fixed potential, a loadimpedance connected between the positive terminal of the source ofpotential and said anode, a cathode impedance including an electrondischarge path having an electron emitter and an electron collectorconnected between the negative terminal of the source of potential andsaid cathode withthe negative terminal of `the source of potentialconnected Ato sa'id electron emitter, a condenser effectively connectedin parallel with said cathode impedance, said electron emitter andelectron collector constituting the only electron conducting pathbetween the negative terminal of the source of potential and saidcathode of the said second amplifying means, the product of the cathodeimpedance and its parallel condenser being substantially equal 4to theproduct of the input circuit resistance and capacitance elements, and anoutput circuit associated with the anode of said second amplifyingmeans.

4. A television signal amplifier for amplifying a Wide frequency band ofsignals comprising an output terminal for supplying the wide frequencyband of signals, an amplifying means having an input circuit, said inputcircuit including a resistance and an effectively parallelly connectedcapacitance, means to apply the signals from the output terminal to theinput circuit of the amplifying means, said amplifying means includingan electron discharge tube having a cathode, a control electrode and ananode, a resistance connected between said control electrode and a pointof Xed potential, means for coupling the input circuit of saidamplifying means to said control electrode, a source of potential havingpositive and negative terminals, means for connecting a point along saidsource of potential to the point of xed potential, a load impedanceconnected between the positive terminal of the source ol potential andsaid anode, a cathode impedance including an electron discharge pathhaving an electron emitter and an electron collector connected betweenthe negative `terminal of the source of potential and said cathode withthe negative terminal of the source of potential connected to saidelectron emitter, a condenser effectively7 connected in parallel withsaid cathode impedance, the product of the cathode impedance and itsparallel condenser being substantially equal to the product of the inputcircuit resistance and capacitance, and an output circuit associatedwith the anode of said tube. f

5. A television signal amplifier for amplifying a wide frequency band ofsignals comprising a source of signals having an output terminal, anamplifying means having an input circuit, said input circuit including aresistance and an effectively parallelly connected capacitance,means toapply the signals from the output terminal to the input circuit of theamplifying means, said amplifying means including an electron dischargetube having a cathode, a control elctrode and an anode, means forcoupling the input circuit to said control electrode, a source ofpotential having positive and negative terminals, a load imelectrondischarge pedance connected between the positive terminal of the sourceof potential and said anode, a cathode impedance including an electrondischarge path having an electron emitter and an electron collectorconnected between the negativeterminal of the source of potential andsaid cathode, a condenser effectively connected in parallel with saidcathode impedance, the prodcondenser being substantially equal to theproduct of the input circuit resistance and capacitance, and'an outputcircuit associated with the tube having a cathode, a control electrodeandV an anode, an input circuit for said amplifying means including aresistance and effectively parallelly connected distributed capacitanceelements, means for applying the signals: to the input circuit of saidamplifying means, a source of potential having positive and negativeterminals, a load impedance connected between the positive terminal ofthe source of potential and said anode, a4 cathode impedance connectedbetween the negative terminal of the source of po-A tential and saidcathode, said caiode impedance having a value substantially equal to theratio of the effective impedance of the input circuit at the lowfrequency end of the band of signals to the effective 4impedance of theinput circuit at the high frequency end of the band of signals, .acondenser effectively connected in parallel with said cathode impedance,the-product of the cathode impedance and its parallel condenser beingsubstantially equal to the product of the input circuit resistance andcapacitance elements, and an output circuit associated with the anode ofsaid electron discharge tube.

7. A television picture signal amplifier for amplifying a wide frequencyband of signals comprising an amplifying means including an electrondischarge tube having acathode, a control electrode and an anode, aninput circuit for said amplifying means including parallelly connectedresistance and capacitance elements, means for applying the signals tothe input circuit of said amplifying means, a source of potential havingVpositive and negative terminals, a load impedance cbnnected between thepositive terminal of the source of potential and said anode, a cathodeimpedance including an electron emitter and an electron collectorconnected between the negative terminal of the source of potential andsaid cathode with the electron emitter connected to the negativeterminal of the source of potential, a condenser effectively connectedin parallel with said cathode impedance, said electron emitter andcollector constituting the only electron conducting path between thenegative terminal of the source of potential and said cathode, theproduct of the cathode impedance and its parallelly connected condenserbeing substantially equal to the product of the input circuit resistanceand capacitance elements, and an output circuit associated with theanode of said electron discharge tube.

8.- A television picture signal amplifier for amplifying a widefrequency band of signals comprising an amplifying means including anelectron discharge tube having a cathode, a control electrode. and ananode, an input circuit for said amplifying means including a resistanceand an effectively parallelly connected capacitance, meansfor applyingthe signals tothe input circuit of said amplifying means, a source ofpotential having positive and negative terminals, a load impedanceconnected between the positive terminal of the source of potential andsaid anode, a cathode impedance including an electron emitter and anelectron collector connected between the negative terminal of the sourceof pouct of the cathode impedance and its parallel u tential and saidcathode with the electron emitter connected to the negative terminal ofthe source of potential, a condenser eifectively connected in parallelwith said cathode impedance, the product of the cathode impedanceand itsparallelly connected condenser being substantially equal to the productof the input circuit resistance and its parallelly connectedcapacitance, and an output circuit associated with the anode of saidelectron discharge tube.

9. `A television signal amplifier for amplifying a wide-frequency bandof signals comprising an amplifying means including an electrondischarge tube having a cathode, a control electrode and an anode, aninput circuit for said amplifying means including a resistance and aneffectively parallelly connected distributed capacitance, means forapplying the signals to the input circuit of said amplifying means, asource of potential having positive and negative terminals, a loadimpedance connected between the positive terminal of the source ofpotential and said anode, a cathode impedance including an elecv secondincluding an amplifying means having a,

tron emitter and an electron collector connected between the negativeterminal of the source of potential and said cathode,V a condensereffectively connected in parallel with said cathode impedance, theproduct of the cathode impedance and its parallel condenser beingsubstantially equal to the product of the input circuit resistance andits parallel capacitance, and an output circuit associated with theanode of said electron discharge tube.

10. An amplifier for amplifying a wide band of frequencies extendingfrom substantially zero to frequencies of the order of many megacyclesper second comprising an amplifying means including an electrondischarge tube having a cathode, a control electrode and an anode, aninput circuit for said amplifying means including parallelly connectedresistance and capacitance elements, a source of potential havingpositive and negative terminals, a load impedance connected between thepositive terminal of the source of p0- tential and said anode, a cathodeimpedance including an electron path having an electron emitter and anelectron collector, means for connecting the electron collector to saidcathode,

means for connecting the electron emitter to the negative terminal ofthe source of potential, a condenser effectively connected in parallelwith said cathode impedance, the product of the cathode limpedance andits parallel condenser being substantially equal to the product of theinput circuit resistance and capacitance elements, and an output circuitassociated with said anode.

11. An amplifier for amplifying a wide band of 4frequencies extendingfrom substantially rzero to frequencies of the order of many megacyclesper second including an amplifying means having a cathode, a controlelectrode and an anode,` an input circuit for amplifying means includingeffectively parallelly connected resistance and capacitance elements, asource of potential having positive and negative terminals, a loadimpedance connected between the positive terminal of the source ofpotential and said anode, a cathode impedance including an electrondischarge path having an electron emitter and an electron collector,means for connecting the electron collector to said cathode, means forconnecting the electron emitter to the negative terminal of the sourceof potential, a condenser effectively connected in parallel with saidcathode impedance, the product ofthe cathode impedance and parallelconcathode, a control electrode and an anode, an input circuit for saidamplifying means including effectively parallelly connected resistanceand capacitance elements, a source of potential having positive andnegative terminals, a load impedance connected between the positiveterminal of the source of potential and said anode, a cathode impedanceincluding an electron discharge path having an electron emitter and anelectron collector, means for connecting the electron collector to saidcathode, means for connecting the electron emitter to the negativeterminal of the source of potential, a condenser effectively connectedin parallel with said cathode impedance, said electron discharge pathconstituting the only electron conducting path beween the negativeterminal of the source of potential and said cathode, and anoutputcircuit associated with said anode. K

13. An amplier circuit including an electron discharge tube having acathode, a control electrode and an anode, means including a resistancefor connecting the control electrode to a point of fixed potential, aninput circuit associated with said control electrode, a source ofpotential having positive and negative terminals, means for connecting apoint along said source of potential to the point of fixed potential, aload impedance connected between said positive terminal of the source ofpotential and said anode, an eifectively high impedance cathode elementcomprising an electron emitter and an electron collector, means fo-rconnecting the electron collector to said cathode, means for connectingthe electron emitter to the negative terminal of the source ofpotential, and an output circuit associated with said anode.

14. An amplifier circuit including a tube having a cathode, a controlelectrode and an anode, an input circuit associated with said controlelectrode, a source of potential having positive and negative terminals,means including a resistance for connecting said control electrode to apoint along said source of potential, a load impedance connected betweensaid positive terminal of the source of potential and said anode, aneffectively Y high impedance cathode circuit including an electronemitter and an electron collector, means for connecting the electroncollector to said cathode, means for connecting the electron emitter tothe negative terminal of the source of potential, and an output circuitassociated with said anode.

15. An amplifier circuit including an amplifying tube having a cathode,a control electrode and an anode, an input circuit connected to saidcontrol electrode, a source of potential having positive and negativeterminals, a, load impedance connected between the positive terminal ofthe source of potential and said anode, an electron discharge tubehaving a cathode, a control electrode and an anode, means for connectingthe anode of the electron discharge .tube to the cathode of theamplifying tube, means for connecting the cathode of said electrondischarge tube to the negative terminal of the source of potential,means to maintain a predetermined bias potential between the controlelectrode and cathode of said electron discharge tube, and an outputcircuit associated with the anode of said amplifying tube.

l 16.- An amplier circuit including an amplifying tube having a cathode,a control electrode and an anode, an input circuit connected to saidcontrol electrode, a source of potential having positive and negativeterminals, a load impedance connected between the positive terminal ofthe source of potential and said anode, an electron discharge pathincluding a cathode, a. control electrode and 10 an anode, means forconnecting the anode of the electron discharge path -to the cathode ofthe amplifying tube, means for connecting the cathode of said electrondischarge path to the negative terminal of the source of potential,means to vary the bias potential between the control. electrode andcathode of said electron discharge path, and an output circuitassociated with said load impedance.

O'I'TO H. SCHADE.

